Process for producing liquid pig iron or liquid steel preproducts and sponge iron as well as a plant for carrying out the process

ABSTRACT

A process for producing liquid pig iron or liquid steel preproducts and sponge iron from iron ore. The iron ore in a first reduction zone (4) is directly reduced to sponge iron. The sponge iron in a meltdown gasifying zone (10) is melted under the supply of carbon carriers and an oxygen-containing gas, and a reducing gas containing CO and H 2  is produced. The reducing gas is introduced into the first reduction zone (4), is reacted there, and is drawn off as an export gas. The drawn-off export gas is subjected to CO 2  elimination as well as heating, and as a reducing gas, at least largely free of CO 2 , is fed to at least one further reduction zone (29) for the direct reduction of iron ore. In order to enable the export gas drawn off the further reduction zone (29) to be utilized as completely as possible, heat of the export gas leaving the further reduction zone (29) is used for heating the export gas derived from the first reduction zone (4).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process and a plant for producing liquid pigiron or liquid steel preproducts and sponge iron from chargingsubstances comprised of iron ore, preferably in lumps and/or pellets,and optionally fluxes. The charging substances in a first reduction zoneare directly reduced to sponge. The sponge iron in a meltdown gasifyingzone is melted under the supply of carbon carriers and anoxygen-containing gas. A reducing gas containing CO and H₂ is produced,which is introduced into the first reduction zone, is reacted there andis drawn off as an export gas. The drawn-off export gas is subjected toCO₂ elimination as well as heating and, as a reducing gas at leastlargely free of CO₂ is fed to at least one further reduction zone forthe direct reduction of further iron ore, After the reaction with theiron ore, the gas is drawn off as an export gas.

2. Description of the Related Art

A process of this type is known, for instance, from DE-C 40 37 977. Inthat known process, export gas drawn off the further reduction zone issubjected to scrubbing and subsequently is subjected to CO₂ eliminationas well as heating together with the export gas derived from the firstreduction zone. This mixed gas is then fed to the further reductionprocess as a reducing gas. Thereby it is feasible to utilize a portionof the reductants still present in the export gas derived from thefurther reduction zone, since that export gas is fed to the furtherreduction process as a recycle reducing gas.

The reducing gas fed to the further reduction process in that knownprocess at first is subjected to preheating in a heat exchanger andsubsequently is heated to the temperature required for the directreduction in a second heating stage, the further heating beingaccomplished by a partial combustion of the reducing gas.

However, such a partial combustion causes deterioration of the qualityof the reducing gas, because reductants are consumed and the CO₂ and/orH₂ O contents are increased. The increase in the CO₂ content to a valuethat is too high may be compensated for by the reducing gas having onlyvery slight contents of CO₂ and H₂ O prior to heating. Yet, thisinvolves the disadvantage that, due to a strict specification with aview to the residual content of CO₂, reductants are discharged alongwith the offgas leaving the CO₂ elimination plant.

SUMMARY OF THE INVENTION

The invention aims at avoiding these drawbacks and difficulties and hasas its object to provide a process, as well as a plant for carrying outthe process, which enable the utilization as complete as possible of theenergy of the export gas derived from the further reduction process, inparticular by saving its reductants. In addition, minimization of theenergy to be externally fed into the further reduction process is to bereached. Moreover, the CO₂ elimination plant is to be operable in anefficient manner, i.e., with a loss of reductants as slight as possible,while nevertheless ensuring sufficiently low CO₂ and H₂ O contents inthe reducing gas fed to the further reduction zone.

In a process of the initially defined kind, this object is achieved inthat heat of the export gas leaving the further reduction zone is usedfor heating the export gas derived from the first reduction zone.

It is a particular object of the invention to use a minimum portion ofexport gas, derived from the further reduction process, for heating thereducing gas fed to the further reduction zone, such that this exportgas will be available to the further reduction process as a recyclereducing gas in an amount as large as possible.

This object is achieved in that, for heating, sensible heat isrecuperatively withdrawn from the export gas drawn off the furtherreduction zone in the hot unscrubbed state, and by means of a heatcarrier, is transmitted to the export gas derived from the firstreduction zone, the heat carrier advantageously being comprised ofscrubbed export gas from the further reduction zone.

For heating the export gas derived from the first reduction process,according to a preferred embodiment, export gas drawn off the furtherreduction zone after scrubbing is recuperatively heated and burned byunscrubbed export gas of the further reduction zone, the smoke gasesrecuperatively heating the export gas derived from the first reductionzone. As a result, the amount of export gas used for combustion isminimized, a greater amount of export gas thus being available torecycling, and a considerable increase in the capacity of the plantfinally being reached.

According to a further preferred embodiment, preheating of the exportgas derived from the first reduction zone is effected by burning exportgas derived from the further reduction zone, and by the recuperativeheat transfer of the heat contained in the smoke gases. Subsequentlyfurther heating is effected by a partial combustion of the export gasderived from the first reduction zone, the thermal energy not consumedin the further reduction process being fed to the partial combustionprocess.

In doing so, oxygen or oxygen-containing gas used for the partialcombustion advantageously is subjected to recuperative heating by meansof chemically bound and/or sensible heat contained in the export gasderived from the further reduction process.

This offers the advantage of minimizing the oxygen consumption and alsoof minimizing the consumption of reducing gas for the partialcombustion. This, in turn, allows for a higher CO₂ specification in thepurified export gas for the CO₂ elimination plant, which results notonly in the further utilization of the residual energy, but also in ahigher-quality reducing gas (containing a higher amount of reductants)and an elevated production output.

These advantages are augmented if at least a portion of the export gasdrawn off the further reduction zone is burned and the smoke gas therebyforming recuperatively gives off sensible heat to the oxygen oroxygen-containing gas, respectively.

An additional enhancement of these advantages may be achieved in that aportion of the preheated export gas drawn off the first reduction zoneis used as a combustion gas along with oxygen and/or anoxygen-containing gas for burning the same.

Furthermore, it is suitable if, for burning export gas derived from thefurther reduction zone, air is admixed to the export gas, which air isrecuperatively heated by smoke gas forming in the combustion of exportgas drawn off the further reduction zone.

A plant for carrying out the process, includes a first reduction reactorfor iron ore, preferably supplied in lumps and/or pellets, and ameltdown gasifier. A supply duct for a reducing gas connects the meltergasifier with the first reduction reactor. A conveying duct for thereduction product formed in the first reduction reactor connects thefirst reduction reactor with the melter gasifier. An export-gasdischarge duct departing from the first reduction reactor. Supply ductsfor oxygen-containing gases and carbon carriers run into the meltergasifier. A tap for pig iron and slag is provided at the meltergasifier. At least one additional reduction reactor receives additionaliron ore. A reducing-gas supply duct is provided to that reductionreactor. An export-gas discharge duct departs from the further reductionreactor, as well as a discharge means for the reduction product formedin that further reduction reactor. The export-gas discharge duct of thefirst reduction reactor runs into a CO₂ elimination plant, from whichthe reducing-gas supply duct of the additional reduction reactor departsand runs into the additional reduction reactor via a heating means forthe export gas purified from CO₂. The export-gas discharge duct of thefurther reduction reactor runs into a heat exchanger and from thereleads to a scrubber. A branch duct branches off the export-gas dischargeduct after that scrubber, runs into the heat exchanger for the purposeof recuperatively heating the branched-off scrubbed export gas by meansof unscrubbed export gas and, departing therefrom, is conducted to theheating means.

It is suitable if the branch duct runs into a burner of the heatingmeans and if the smoke gas of the burner, by means of a smoke-gas ductvia a heat exchanger, is conducted to the recuperative heating of anoxygen-containing gas or oxygen fed to the heating means via the duct.

Preferably, the branch duct runs into a burner of the heating means andthe smoke gas of the burner is fed to the recuperative heating of anoxygen-containing gas, such as air, by means of a smoke-gas dischargeduct via a heat exchanger, the heated air being fed to the burner of theheating means via a duct.

A preferred embodiment is characterized in that a branch duct departsfrom the reducing-gas supply duct after the heat exchanger serving toheat the reducing gas fed to the further reduction reactor, and runsinto an afterburning means together with a duct supplying oxygen or anoxygen-containing gas.

Another preferred plant comprises a first reduction reactor for ironore, preferably supplied in lumps and/or pellets, and a melter gasifier.A supply duct for a reducing gas connects the melter gasifier with thefirst reduction reactor. A conveying duct for the reduction productformed in the first reduction reactor connects the first reductionreactor with the melter gasifier. An export-gas discharge duct departsfrom the first reduction reactor. Supply ducts for oxygen-containinggases and carbon carriers run into the melter gasifier. A tap for pigiron and slag is provided at the melter gasifier. At least oneadditional reduction reactor for receives additional iron ore. Areducing-gas supply duct is provided to that reduction reactor. Anexport-gas discharge duct departs from the further reduction reactor, aswell discharge means for the reduction product formed in that furtherreduction reactor. The export-gas discharge duct of the first reductionreactor runs into a CO₂ elimination plant, from which the reducing-gassupply duct of the additional reduction reactor departs and runs intothe additional reduction reactor via a heating means for the export gaspurified from CO₂. From the export-gas discharge duct of the furtherreduction reactor, a branch duct runs into a burner of the heatingmeans. That smoke gas of the burner, by means of a smoke-gas dischargeduct, via a heat exchanger, is conducted to the recuperative heating ofan oxygen-containing gas, such as air, or of oxygen, and the heatedoxygen-containing gas or the oxygen, respectively, is conducted to theheating means via a duct.

Suitably, the heated oxygen-containing gas or the heated oxygen getsinto an afterburning means of the heating means together with reducinggas fed via a branch duct departing from the reducing-gas supply duct.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be explained in more detail by wayof several exemplary embodiments, FIGS. 1 to 6 each illustrating aprocess variant represented in a block diagram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a first reduction reactor designed as a shaft furnace 1 particulateiron-oxide-containing material, preferably lumpy iron ore, and possiblefluxes are supplied by means of a duct 2 in a known manner as inaccordance with FIGS. 1 to 4. Reducing gas is blown into the reductionshaft furnace 1 by means of a supply duct 3 so as to rise upwardly incounter-flow to the descending iron ore, effecting the reduction of thecharge in the reduction zone 4. After having flown through the shaftfurnace 1, that gas is discharged as an export gas by means of anexport-gas discharge duct 5. The reduced burden, which contains iron inthe form of sponge iron, gets into a melter gasifier 7 via conveyingducts preferably designed as downpipes 6. A lumpy carbon carrier, forinstance in the form of brown-coal high-temperature coke as well asoptionally coal, through a duct 8 and, furthermore, an oxygen-containinggas through a duct 9, are supplied to the melter gasifier 7 in a knownmanner.

By "sponge iron" a solid final or intermediate product is meant, whichis formed of an iron oxide by direct reduction exclusively via the solidphase, i.e., without it being necessary to follow a path via a liquidintermediate product.

In the meltdown gasifying zone 10 formed within the melter gasifier 7the burden or sponge iron falls from top onto a fluidized bed formed oflumpy carbon carriers and maintained by the oxygen-containing gas blownin. By burning the coke as well as optionally the coal under the actionof the oxygen-containing gas, so much heat is produced in the fluidizedbed that the sponge iron is melted. In the molten state, it iscompletely reduced by means of carbon such that a pig iron melt or steelpreproduct collects on the bottom of the melter gasifier 7 in the liquidstate. A slag melt forms above the pig iron melt. Those two melts aredrawn off via appropriately arranged taps 11, 12 at predetermined timeintervals.

During the combustion of coke and optionally coal in the melter gasifier7, a reducing gas essentially consisting of CO and H₂ is produced, whichis drawn off the melter gasifier 7 via the supply duct 3 and fed to thereduction shaft furnace 1. The purification and cooling of the reducinggas formed in the melter gasifier 7 to the temperature required fordirect reduction in a manner known per se is effected via dustseparators or scrubbers, which, however, is not illustrated in detail inthe drawing.

The export gas drawn off through the export-gas discharge duct 5 atfirst is subjected to purification, for instance, in a cyclone 13 or ina scrubber in order to be freed from dust particles. After this, theexport gas, by means of a compressor 14, reaches a CO₂ elimination plant15, in which it is largely freed from CO₂ and, at the same time, from H₂S. The CO₂ elimination plant is designed, for instance, as a pressureswing adsorption plant or as a CO₂ scrubber.

The thus purified export gas as a reducing gas is fed to a furtherreduction reactor via a reducing-gas supply duct 16, which furtherreduction reactor is designed as a reduction shaft furnace 17 and, likethe first reduction shaft furnace 1, is operated according to thecounterflow principle. In that shaft furnace 17 particulate ore suppliedvia the ore-supply duct 18 is directly reduced. A discharge means forsponge iron formed in the shaft furnace 17 from the ore is denoted by19.

Since the export gas destined for the purification of CO₂ is to becooled to a temperature level required therefor, it is subjected toheating prior to being introduced into the further reduction shaftfurnace 17. Heating is effected in two stages: At first, the purifiedexport gas in a first stage is subjected to indirect heating, theheating means 20 serving that purpose being designed as a heatexchanger. The heat exchanger (recuperator) 20 comprises a burner 21 towhich there is fed as a combustion gas an oxygen-containing gas, such asair, via a duct 22 and purified export gas drawn off the furtherreduction shaft furnace 17 and supplied via a branch duct 23. Heatingwithin the heat exchanger 20 is effected to a temperature justcompatible with the tube material. After this, the reducing gasrecuperatively heated in the first stage is further heated in a secondstage to the reducing gas temperature required for reduction by partialcombustion in the afterburning means 24, in which a portion of theexport gas purified from CO₂ and branched off the reducing-gas supplyduct 16 via a branch duct 16' is burned under oxygen supply 25. In doingso, highly pure oxygen is used, the reducing gas thereby attaining thetemperature required for the reduction in the further reduction shaftfurnace 17 by means of a minimum amount of export gas to be burned. Thetemperature required ranges between 600° and 900° C.

The export gas drawn off the reduction shaft furnace 17 via theexport-gas discharge duct 26 likewise is subjected to purification andcooling in a scrubber 27 in order to be purified from dust particles andcause its water vapor content to be lowered. After this, a portion ofthe purified export gas is branched off via the branch duct 23 andsupplied to the burner 21 of the heat exchanger 20. This branch duct 23is conducted via a heat exchanger 28 arranged between the reductionshaft furnace 17 and the scrubber 27 and penetrated by hot export gasfrom the further reduction process, that portion of purified export gasthus recuperatively experiencing a considerable increase in temperature.Consequently, only a slight amount of the export gas from the furtherreduction zone 29 of the reduction reactor 17 need be supplied to theburner 21, that portion of the export gas having been brought to a highenergy level by aid of the sensible heat of the export gas drawn off thereduction shaft furnace 17.

A further portion of the export gas incurring in the further reductionshaft furnace 17 via a compressor 30 is fed also to the CO₂ eliminationplant 15 through a conveying duct 31 running into the export-gasdischarge duct 5, hence likewise being available to the CO₂ eliminationplant and subsequently to the further reduction process as a recyclereducing gas. That portion of the export gas from the reduction shaftfurnace 17 which is not required for the process according to theinvention is supplied as an export gas through the export-gas dischargeduct 26.

The CO₂ -containing offgas separated from the CO₂ elimination plant 15via an offgas duct 32 suitably is admixed to that portion of the exportgas which has been supplied to the burner 21 of the heat exchanger 20through the branch duct 23, advantageously before that branch duct 23passes through the heat exchanger 28. Into the export-gas discharge duct26 there may also run a branch duct 33 branching off the offgas duct 32and optionally comprising a desulfurization means 34, by means of whichbranch duct a portion of the CO₂ -containing offgas is admixed with theexport gas.

According to the variant represented in FIG. 1, the smoke gas formed inthe burner 21 of the heat exchanger 20 is conducted away through asmoke-gas discharge duct 35, a heat exchanger 36 for heating oxygenbeing provided in the smoke-gas discharge duct 35. That oxygen is fed tothe partial combustion process taking place in the afterburning means24, by means of the oxygen supply 25. By heating the oxygen, aminimization of the oxygen consumption and also a minimization of theconsumption of reducing gas used for the partial combustion arefeasible.

According to the process variant represented in FIG. 2, air isadditionally heated by means of a further heat exchanger 37 provided inthe smoke-gas discharge duct, by aid of the smoke gas formed in theburner 21 of the heat exchanger 20, the heated air being fed to theburner 21 of the heat exchanger 20 through duct 22. Thereby, the amountof export gas fed to the burner 21 of the heat exchanger 21 can befurther reduced.

According to the process variant represented in FIG. 3, reducing gaspreheated in the heat exchanger 20--this being branched off by means ofa branch duct 16"--is used for the partial combustion taking place inthe afterburning means 24 such that sensible heat of the smoke gasformed in the burner 21 of the heat exchanger 20 is made available tothe partial combustion not only via the oxygen fed, but also via thereducing gas provided for the partial combustion. Hence the optimumutilization of residual heat is achieved, which is reflected not only byan enhanced quality of the reducing gas, but also by an increase inproduction.

FIG. 4 illustrates a simplified process variant, in which the export gasfed to the burner 21 of the heat exchanger 20 and derived from thefurther reduction process is fed into a heat exchanger 20 withoutprevious heating. In that process variant, merely the sensible heatcontained in the smoke gas is utilized for heating the oxygen fed to thepartial combustion.

FIG. 5 depicts a variant of the process illustrated in FIG. 1, theprocess according to FIG. 5 differing from the process according to FIG.1 in that the export gas branched off by means of the branch duct 23 isno longer conducted via the heat exchanger 28, but is conveyed directlyto the burner 21 of the heat exchanger 20. Thereby, the calorific valueof the branched-off export gas is preserved, that high-quality exportgas being available to the burner 21 as an assistant combustion gas.Since the offgas of the CO₂ elimination plant 15 carried away in theoffgas duct 32 is no longer mixed with the export gas branched off viathe branch duct 23, but is heated in the heat exchanger 28 in theunmixed state, it reaches a higher temperature level; it is fed to theburner 21 separate from the branched-off export gas. This embodimentoffers the advantage that the pressure loss in the branch duct 23 islower than in the variant illustrated in FIG. 1, because duct 23 is nolonger conducted through the heat exchanger 28. It is true that theoffgas derived from the CO₂ elimination plant 15 in the embodimentrepresented in FIG. 5 is no longer fattened by the branched-off exportgas such that its inflammability is not enhanced, yet this is by farcompensated for by improving the limits of inflammability of that offgasby means of the enhanced temperature increase occurring in the heatexchanger 28 in combination with an assistant burner operated by thebranched-off export gas.

According to the variant illustrated in FIG. 6, of the process accordingto the invention represented in FIG. 4, the export gas branched off bymeans of the duct 23 likewise is no longer mixed with the offgas fromthe CO₂ elimination plant 15, but both gases are fed to the burner 21 ofthe heating means 20 separately, the branched-off export gas againassuming an assistant burning function.

The invention is not limited to the exemplary embodiments dealt with inthe description of the Figures, but may be modified in various aspects.It is, for instance, possible to provide for a reduction of fine ore byfluidization instead of the shaft furnace 1 being operated according tothe fixed bed method, i.e., to replace the shaft furnace 1 with one orseveral fluidized bed reactors. The same holds for the further reductionprocess, i.e., also the reduction shaft furnace 17 may be replaced withfluidized bed reactors in which fine ore is reduced by fluidization.

Furthermore, it may be advantageous if the heat exchanger 36 for heatingoxygen precedes the heat exchanger 20 such that the hot gases forming inthe burner 21 heat the oxygen first and the purified export gas onlyafterwards. Thereby, the oxygen may be heated to higher temperatures andhence used in smaller quantities. This offers the additional advantagethat less CO and H₂ are reacted in the afterburning means 24 such thatthe ratios of CO/CO₂ and H₂ /H₂ O may be improved even further.

The improvements in the CO/CO₂ and H₂ /H₂ O ratios during the reactionoccurring in the afterburning means 24 are explained by way of thefollowing examples:

In a plant according to FIG. 1, in which, however, the heat exchanger 20for heating the export gas is preceded by the heat exchanger 36 forheating oxygen as described above--the hot combustion gas formed in theburner 21 flowing through the heat exchanger 36 first and through theheat exchanger 20 only afterwards--the export gas derived from the firstreduction zone 4 has a temperature of 45° C. immediately before itsintroduction into the heat exchanger 20. A portion of that export gas isbranched off and fed to the afterburning means 24 at that temperature.

Oxygen preheated to 500° C. in the heat exchanger 36 via duct 25likewise is conveyed to the afterburning means 24, in which a hot gas of4,755° C. is generated by combustion. That hot gas in the afterburningmeans 24 is mixed with export gas heated to 514° C. in the heatexchanger 20 such that finally a reducing gas having a temperature ofabout 800° C. is formed, which is fed to the further reduction shaftfurnace 17 by means of the reducing-gas supply duct 16.

In view of the prior art, according to which oxygen is supplied to theafterburning zone at room temperature, an increase in quality isobtained by the fact that less oxygen must be fed to the afterburningmeans 24 and hence less CO and H₂ must be reacted during combustion. Asa result, the CO/CO₂ ratio has been improved by approximately 1.4% andthe H₂ /H₂ O ratio by approximately 3.3%.

In a plant according to FIG. 3, export gas again having a temperature of45° C. reaches the heat exchanger 20 and there is heated to atemperature of 514° C. and is supplied to the afterburning means 24 atthat temperature. A portion of the thus heated export gas is fed to theafterburning means 24 through duct 16", together with oxygen heated to250° C. in the heat exchanger 36, and is burned. Thereby, a hot gashaving a temperature of 4,996° C. is formed, from which a reducing gashaving a temperature of 801° C. results.

Also in that case the amount of oxygen fed can be reduced, henceresulting a CO/CO₂ ratio enhanced by 3.2% as opposed to the prior art.The H₂ /H₂ O ratio has been improved by 7.8% .

If, in accordance with the above-described exemplary embodimentaccording to FIG. 3, the heat exchanger 20 is preceded by the heatexchanger 36 such that the hot gases conducted in the burner 21 flowthrough the heat exchanger 36 first and through the heat exchanger 20only afterwards, heating of the oxygen to 500° C. is feasible so thatthe latter may be further reduced in terms of quantity for thecombustion taking place in the afterburning means 24. By burning, bymeans of the thus heated oxygen, a portion of the export gas heated to514° C., a hot gas having a temperature of 5,051° C. forms, which uponmixing with the residual export gas heated to 514° C., brings about areducing gas having a temperature of 800° C. and an improvement in theCO/CO₂ ratio by 3.9%. The H₂ /H₂ O ratio has been improved by 8.9%.

In the following, the advantage of heating in the heat exchanger 28 theCO₂ -containing offgas separated from the CO₂ elimination plant 15 bymeans of the offgas duct 32 will be explained, wherein, however,exclusively CO₂ -containing offgas and no export gas emerging from thefurther reduction shaft furnace 17 via duct 26 is heated in the heatexchanger 28. The CO₂ -containing offgas separated from the CO₂elimination plant 15 has a temperature of 45° C. and is heated in theheat exchanger 28 to a temperature of about 280° C. in order to increaseits inflammability. Such heating of the offgas has the advantage thatexport gas from the further reduction process need not be supplied anymore for burning the same.

The CO₂ -containing offgas thus heated to 280° C. is supplied to theburner 21 through duct 23 and there is burned by means of non-preheatedair, i.e., air having a temperature of about 25° C. In doing so, a hotgas having a temperature of 851° C. is formed, by aid of which exportgas from the first reduction process may be heated in the heat exchanger20. By such heating of the CO₂ -containing offgas to above inflammationtemperature, it is feasible to recirculate the export gas incurring inthe further reduction process completely via the duct 31, thus fullyutilizing the same for direct reduction.

Although the present invention has been described in relation toparticular embodiments thereof,many other variations and modificationsand other uses will become apparent to those skilled in the art.Therefore, the present invention is to limited not by the specificdisclosure herein, but only by the appended claims.

We claim:
 1. A process for producing liquid pig iron or liquid steelpreproducts and sponge iron from charging substances of iron ore,whereinthe charging substances in a first reduction zone are directly reducedto sponge iron, the sponge iron in a meltdown gasifying zone is meltedunder a supply of carbon carriers and an oxygen-containing gas and areducing gas containing CO and H₂ is produced, which is introduced intothe first reduction zone, is reacted there and is drawn off as an exportgas, and wherein the drawn-off export gas is subjected to CO₂elimination as well as heating to produce export gas at least largelyfree of CO₂ which is fed to at least a second reduction zone for directreduction of further iron ore and after the reaction with the iron oreis drawn off as an export gas from the second reduction zone, whereinheat of the export gas drawn off the second reduction zone is used forheating the export gas derived from the first reduction zone.
 2. Aprocess according to claim 1, wherein, for heating, sensible heat isrecuperatively withdrawn from the export gas drawn off the secondreduction zone in a hot unscrubbed state and by means of a heat carrieris transmitted to the export gas derived from the first reduction zone.3. A process according to claim 2, wherein the heat carrier is comprisedof scrubbed export gas of the second reduction zone.
 4. A processaccording to claim 3, wherein, for heating the export gas derived fromthe first reduction zone, export gas drawn off the second reduction zoneafter scrubbing is recuperatively heated, and burned, by unscrubbedexport gas of the second reduction zone, the smoke gases recuperativelyheating the export gas derived from the first reduction zone.
 5. Aprocess according to claim 1, wherein preheating of the export gasderived from the first reduction zone is effected by burning export gasderived from the second reduction zone and by recuperative heat transferof the heat contained in the smoke gases, and subsequently furtherheating is effected by a partial combustion of the export gas derivedfrom the first reduction zone, the thermal energy not consumed in thesecond reduction zone being fed to said partial combustion of the exportgas.
 6. A process according to claim 5, wherein one of oxygen oroxygen-containing gas used for said partial combustion is subjected torecuperative heating by means of chemically bound and/or sensible heatcontained in the export gas derived from the second reduction zone.
 7. Aprocess according to claim 6, wherein at least a portion of the exportgas drawn off the second reduction zone is burned and the smoke gasthereby forming recuperatively gives off sensible heat to the oxygen oroxygen-containing gas, respectively.
 8. A process according to claim 5,wherein portion of the preheated export gas drawn off the firstreduction zone is used as a combustion gas along with one of oxygen oran oxygen-containing gas for burning the export gas.
 9. A processaccording to claim 4, wherein, for burning export gas derived from thesecond reduction zone, air is admixed to said export gas, which air isrecuperatively heated by smoke gas forming in the combustion of exportgas drawn off the second reduction zone.
 10. A plant for carrying outthe process according to claim 1, the plant comprising:a first reductionreactor for iron ore; a melter gasifier; a supply duct for a reducinggas, the supply duct connecting the melter gasifier with the firstreduction reactor; a conveying duct for a reduction product formed inthe first reduction reactor and connecting the first reduction reactorwith the melter gasifier; an export-gas discharge duct departing fromthe first reduction reactor; supply ducts for oxygen-containing gasesand carbon carriers running into the melter gasifier; a tap for pig ironand slag provided at the melter gasifier; at least a second reductionreactor for receiving additional iron ore; a reducing-gas supply ductconnected to said second reduction reactor; an export-gas discharge ductfrom said second reduction reactor; a discharge means for a reductionproduct formed in said second reduction reactor; and a CO₂ eliminationplant; wherein the export-gas discharge duct of the first reductionreactor runs into the CO₂ elimination plant; and the reducing-gas supplyduct of the second reduction reactor departs from the CO₂ eliminationplant and runs into the second reduction reactor via a heating means forthe export gas purified from CO₂, and wherein the export-gas dischargeduct of the second reduction reactor runs into a heat exchanger and fromthere leads to a scrubber; and a branch duct branches off the export-gasdischarge duct after said scrubber and runs into the heat exchanger forrecuperatively heating the branched-off scrubbed export gas by means ofunscrubbed export gas and, departing therefrom, is conducted to theheating means.
 11. A plant according to claim 10, wherein the branchduct runs into a burner of the heating means and smoke gas of theburner, by means of a smoke-gas discharge duct via a heat exchanger, isconducted to recuperative heating of one of an oxygen-containing gas oroxygen fed to the heating means.
 12. A plant according to claim 10,wherein the branch duct runs into a burner of the heating means andsmoke gas of the burner is fed to recuperative heating of anoxygen-containing gas by means of a smoke-gas discharge duct via a heatexchanger, the heated air being fed to the burner of the heating means.13. A plant according to claim 10 wherein a branch duct departs from thereducing-gas supply duct after the heat exchanger serving to heat thereducing gas fed to the second reduction reactor and runs into anafterburning means together with a duct supplying one of oxygen or anoxygen-containing gas.
 14. A plant for carrying out the processaccording to claim 1, the plant comprising:a first reduction reactor foriron ore; a melter gasifier; a supply duct for a reducing gas connectingthe melter gasifier with the first reduction reactor; a conveying ductfor a reduction product formed in the first reduction reactor andconnecting the first reduction reactor with the melter gasifier; anexport-gas discharge duct departing from the first reduction reactor;supply ducts for oxygen-containing gases and carbon carriers runninginto the melter gasifier; a tap for pig iron and slag provided at themelter gasifier; a second reduction reactor for receiving additionaliron ore; a reducing-gas supply duct connected to said second reductionreactor; an export-gas discharge duct departing from said secondreduction reactor; a discharge means for a reduction product formed insaid second reduction reactor; a CO₂ elimination plant connected to saidsecond reduction reactor and producing export gas purified of CO₂ ; anda heating means for heating the export gas purified of CO₂, the heatingmeans having a burner, wherein the export-gas discharge duct of thefirst reduction reactor runs into the CO₂ elimination plant, and thereducing-gas supply duct of the additional reduction reactor departsfrom the CO₂ elimination plant and runs into the second reductionreactor via the heating means for the export gas purified of CO₂, andwherein a branch duct runs from the export-gas discharge duct (26) ofthe second reduction reactor into the burner of the heating means, andthe smoke gas of the burner, by means of a smoke-gas discharge duct andvia a heat exchanger, is conducted to recuperative heating of one of anoxygen-containing gas or oxygen and the heated oxygen-containing gas oroxygen is conducted to the heating means via a duct.
 15. A plantaccording to claim 14, wherein the heated oxygen-containing gas oroxygen is fed to an afterburning means of the heating means togetherwith reducing gas fed via a branch duct departing from the reducing-gassupply duct.
 16. A merchantable product, made of pig iron or steelpreproducts produced by a process according to claim
 1. 17. A processfor producing liquid pig iron or liquid steel preproducts and spongeiron from charging substances of iron ore, comprising the stepsof:directly reducing the charging substances to sponge iron in a firstreduction zone; melting the sponge iron in a meltdown gasifying zoneunder a supply of carbon carriers and an oxygen-containing gas toproduce a reducing gas containing CO and H₂ ; introducing the reducinggas into the first reduction zone; reacting the reducing gas in thefirst reduction zone; drawing off the reducing gas from the firstreduction zone as an export gas; subjecting the drawn-off export gas toCO₂ elimination, as well as heating, to produce a reducing gas at leastlargely free of CO₂ ; drawing off the reducing gas at least largely freeof CO₂ ; feeding the reducing gas at least largely free of CO₂ to atleast one further reduction zone for the direct reduction of furtheriron ore and after the reaction with the iron ore is drawn off as anexport gas; and heating the export gas derived from the first reductionzone using heat of the export gas leaving the further reduction zone.18. A process according to claim 1, wherein the export gas drawn off thesecond reduction zone and used for heating the export gas derived fromthe first reduction zone is a minimum portion, remaining export gasbeing available as a recycle gas in an amount as large as possible. 19.A process according to claim 17, wherein the export gas drawn off thefurther reduction zone and used for heating the export gas derived fromthe first reduction zone is a minimum portion, remaining export gasbeing available as a recycle gas in an amount as large as possible.